The invention relates to a method for carrying out nuclear magnetic resonance measurements on a sample using a first working volume and second working volume with different magnetic field strengths.
Such a method is known from U.S. Pat. No. 8,154,292 B2.
Nuclear magnetic resonance (=NMR) spectroscopy is a powerful tool in instrumental chemical analysis. In NMR experiments, a sample is exposed to a strong static magnetic field which interacts with spins of nuclei contained in the sample. Radio frequency (=RF) pulses are sent into the sample for manipulating the spins, and the sample's reaction, i.e. RF signals (also called NMR signals) are measured. The sample's reaction depends on the environment of the nuclei in the sample, in particular bonding electrons. Accordingly, information about the chemical structure of the sample can be obtained by analyzing the RF signals measured.
In general, stronger static magnetic fields lead to stronger NMR signals and higher resolution, what improves the quality of information obtained from the sample. However, providing very strong magnetic fields is complex and expensive. Moreover, for some types of experiments, stronger magnetic fields do not offer improvements, in particular when chemical shift anisotropy becomes relevant, e.g. in carbonyl 13C relaxation. Further, in experiments including chemical shift evolution delays, there are optimum magnetic fields for some nuclei which are already accessible, so further increase of magnetic field strength will not improve the quality of information obtained from the experiment here.
In order to improve NMR signal strength, it is known to apply hyperpolarization to the nuclei to be investigated. In U.S. Pat. No. 8,154,292 B2, a DNP-NMR apparatus is disclosed, which comprises a first working volume at a center of a superconducting magnet configuration, equipped with an NMR probe, and a second working volume at a distance form the first working volume and with magnetic field strength lower than at the first working volume, equipped with a device for DNP (dynamic nuclear polarization) excitation. Both working volumes are located in the room temperature bore of a cryostat containing the superconducting magnet configuration. A transfer mechanism allows movement of a sample between the working volumes. This apparatus allows doing the DNP polarization at a dedicated location, independent of the actual NMR experiment.
R. Kreis at al., Chem. Phys. Lett. Vol. 118, No. 2, Jul. 19, 1985, pages 120-124, describe a time domain zero-field magnetic resonance experiment with field pulse excitation. A sample is polarized in high magnetic field, then rapidly transported to zero field by a gas pressure system. At zero field, RF pulses are applied to the sample. The sample is then transferred back to high field, and NMR detection is done by applying an echo sequence using composite π/2 pulses. This experiment is useful if electrical fields alone, which cause different energy levels for different nuclear spins, shall be studied, for example electrical quadrupole fields.
It is the object of the invention to provide a method for doing NMR experiments with which more and/or improved quality information about an investigated sample can be obtained.